1. Field of the Invention
The present invention relates to a hydrogen storage alloy electrode, particularly suitable for use as a negative electrode of alkaline storage cells or batteries, and to a method for fabrication of the hydrogen storage alloy electrode.
2. Related Art
A nickel-hydrogen storage cell or battery is regarded as a prime candidate for the alkaline battery of the next generation, because of its high capacity, more than twice of that of a nickel-cadmium battery, and its environmentally friendly nature.
Such alkaline batteries typically use a hydrogen storage alloy electrode. There generally exists two types of hydrogen storage alloy electrodes; a sintered hydrogen storage alloy electrode prepared by sintering hydrogen storage alloy powder, and a pasted hydrogen storage alloy electrode prepared by coating or loading a paste containing hydrogen storage alloy powder particles on or in an electrically conductive core. However, these two types of hydrogen storage alloy electrodes suffer from a common deficiency. As the electrode undergoes a change in its volume during the charge-discharge cycles, the hydrogen storage alloy powder incorporated therein is often subjected to subdivision to result in the occurrence of falling-off or shedding of the subdivided powder particles. This has led to the reduced initial discharge capacities as well as the shortened charge-discharge cycle lives of alkaline batteries using those hydrogen storage alloy electrodes.
In order to overcome the above-described deficiency, a method has been proposed, for example in Japanese Patent Laying-Open No. 60-70665 (1985), which utilizes hydrogen storage alloy powder of smaller particle sizes. The use of the size-reduced hydrogen storage alloy powder results in the reduced occurrence of subdivision, so that the shedding of powder particles is effectively suppressed. Fabrication of an electrode from the size-reduced hydrogen storage alloy powder, in accordance with the proposed method, allows for a large electrode surface area. An alkaline storage battery using such an electrode is thus expected to produce a high level of discharge capacity.
However, the size-reduced hydrogen storage alloy powder is readily oxidized in the air to produce electrically inert surface films, such as oxide films. Accordingly, an alkaline storage battery incorporating such a hydrogen storage alloy powder in its negative electrode fails to enjoy the expected improvements in cycle life and discharge characteristics. In addition, the failure to suppress the generation of hydrogen gas during charge leads to an unfavorable pressure build-up in the battery.